U.S. Pat. No. 4,674,834 issued June 23, 1987 to G. D. Margolin and assigned to the assignee of the present application discloses a fiber optic technology for implementing document scanners and scopes. The technology utilizes a noncoherent fiber optic bundle where the entrance field is constrained into an ideally linear geometry to correspond to the width of a document to be scanned. The exit field of the bundle is constrained into a rectangular geometry and fixed with respect to a sensor array of like geometry. The sensor array is composed of discrete sensors which can be accessed conveniently on a random access basis.
Because there is no positional correspondence between fiber ends in the entrance field and the fiber ends of corresponding fibers in the exit field, that positional information has to be obtained. The information is obtained by what can be visualized as asking each fiber where its exit end is with respect to the sensor array.
The positional information is obtained by passing light into the fibers of the entrance field one at a time and interrogating the sensor array to ascertain the address of the illuminated sensor in each instance. In this manner, a sensor address can be assigned to correspond to the exit position of a fiber which has its input end illuminated. By repeating this procedure, an address string is formed which, when clocked, produces the sequence of exit positions (i.e. the corresponding addresses) for the sequence of fiber ends in the entrance field.
The "initialization" procedure is simple to visualize as described, but it cannot be implemented so easily. It is very difficult to move a beam to the position of a fiber end in the entrance field. The fibers are tiny (a fraction of the size of a human hair) and their locations are not known. They are constrained to an ideally linear arrangement but they are unevenly spaced, laterally displaced and bunched up. A simple procedure for initialization is disclosed in co-pending application Ser. No. 894,792 filed Aug. 8, 1986 and also assigned to the assignee of the present application.
In any case, a string of sensor addresses is formed for organizing the pixels transmitted by the fiber optic bundle. That string of addresses is used to interrogate only those addresses of the sensor array if the array is organized on a random access basis. The string of addresses may be used to define the sequence of significant addresses if the entire memory is to be read out as would be the case with a CCD sensor array.
This initializing technique also is useful for a coherent fiber optic bundle which is coupled to an array of discrete sensors at its exit end. Although such an operation would be considered useless because all the positional information is already known for coherent bundles, problems do occur with such bundles when coupled to an array of discrete sensors. Specifically, if the fiber size is greater than the sensor size, defects occur in the image. The defects are due to aliasing, Moire patterns, misalignment as well as size differences. All such defects are eliminated by initialization. The initialization of coherent fiber optic bundles also is disclosed in the above-mentioned co-pending patent application.
In a typical implementation of a document scanner with a fiber optic bundle, thousands of fibers are employed over an eight and one-half inch linear entrance field. If five thousand fibers are used and, all fibers are usable, about six hundred bits per inch (bpi) resolution can be achieved. But it is clear that one hundred bpi, two hundred bpi, two hundred forty bpi, three hundred bpi, four hundred and eighty bpi, etc. are also desirable for speed and compatibility consideration. This invention is directed at a simple arrangement for achieving different resolution levels with a single fiber optic scanner.